Nano-diamond dispersion solution and method for preparing same

ABSTRACT

The present invention relates to a nano-diamond dispersion solution and a method of preparing the same. The method of preparing a nano-diamond dispersion solution comprises the following steps: providing a nano-diamond aggregation; mixing the nano-diamond aggregation with a metal hydroxide solution and stirring the mixture such that the nano-diamond aggregation is separated, to obtain a mixture solution; stabilizing the mixture solution such that the mixture solution is separated into a supernatant and precipitates; and extracting the supernatant and precipitates.

TECHNICAL FIELD

The present invention relates to a nano-diamond dispersion solution anda method of preparing the same, and more particularly, to a nano-diamonddispersion solution of uniformly distributed nano-diamond particleshaving a size of several nanometers to several tens of nanometers.

CROSS-REFERENCE TO THE RELATED APPLICATIONS

This application is the U.S. national stage application under 35 U.S.C.§371 of International Application No. PCT/KR2011/000957, filed Feb. 11,2011, which claims the benefit of Korean Patent Application No.10-2010-0013485, filed on Feb. 12, 2010, and Korean Patent ApplicationNo. 10-2011-0011931, filed on Feb. 10, 2011, in the Korean IntellectualProperty Office, the disclosures of which are incorporated herein intheir entirety by reference.

BACKGROUND ART

Due to advantages such as high hardness, transmittance of broadbandlight, chemical stability, high thermal conductivity, low thermalexpansion, electrical insulating properties, biocompatibility, andeco-friendliness, nano-diamond is applicable in a variety of industrialfields such as the electronic, chemical, and medical industries.Synthetic diamond powder having a size of micrometers has been widelyused in many industries.

With recent breakthroughs in nanotechnology, research into nano-diamondhaving a very small particle diameter has been conducted. Nano-diamondparticles having an average particle diameter of from about 5 nm toabout 10 nm may be obtained in a very short explosion time under anextremely high pressure.

Nano-diamond particles prepared to have an average particle diameter offrom about 5 nm to about 10 nm are nano-diamond aggregations withsurfaces covered with a disordered graphite layer. These nano-diamondparticle aggregations may have a variety of chemical and structuralcharacteristics depending on a chemical treatment method.

Nano-diamond has unique electrical, chemical, and opticalcharacteristics, such as small particle size, large surface area, highmechanical strength, and adjustable surface activity. However,nano-diamond particles tend to form aggregations due to increasedattraction between particles resulting from a large surface area, andthus there is a limit to prepare nano-diamond having a particle diameterof tens of nanometers or less.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

The present invention provides a method of preparing a nano-diamonddispersion of uniformly dispersed nano-diamond particles having a sizeof several is nanometers to tens of nanometers.

The present invention provides a nano-diamond dispersion prepared usingthe method.

The present invention provides a sealing agent for anodization, aplating additive, a polishing agent, an oil additive, a polymer resinadditive, and a heat-dissipating additive that each include thenano-diamond dispersion prepared using the above-described method.

Technical Solution

According to an aspect of the present invention, there is provided amethod of preparing a nano-diamond dispersion, the method including:providing a nano-diamond aggregation; mixing the nano-diamondaggregation and an aqueous metal hydroxide solution while agitating toprepare a mixture solution in order to disintegrate the nano-diamondaggregation; stabilizing the mixture solution to be separated into asupernatant and a precipitate; and extracting the supernatant and theprecipitate respectively from the mixture solution.

The method may further include, after the extracting of the supernatantand the precipitate from the mixture solution, drying the supernatant toobtain nano-diamond powder; and mixing the nano-diamond powder with adispersion solvent.

The method may further include, after the extracting of the supernatantand the precipitate from the mixture solution, adding the precipitateback into the mixture solution while agitating.

The preparing of the mixture solution may further include disintegratingthe nano-diamond aggregation using a centrifuge, a ball mill, a beadmill, or an ultrasonicator.

The aqueous metal hydroxide solution may include at least one ofpotassium (K), calcium (Ca), sodium (Na), magnesium (Mg), aluminum (Al),zinc (Zn), iron (Fe), nickel (Ni), tin (Sn), and lead (Pb).

The aqueous metal hydroxide solution may be NaOH, KOH, or a mixturethereof.

The preparing of the mixture solution may include chemically binding ametal ion is in the aqueous metal hydroxide solution and a reactivegroup in the nano-diamond aggregation.

The reactive group may include at least one of a carboxyl group (—COOH),a hydroxyl group (—OH), an alcohol group (CH₂OH), an amine group (—NH₂),an amide group (—NHCOCH₃), an amide group (—CONH), a sulfone group(COSO₃H), a sulfonyl chloride group (COSO₂Cl), a methyl group (—CH₃), analdehyde group (—CHO), and an ether group (—O—).

According to an aspect of the present invention, there is provided anano-diamond dispersion prepared using any of the above-describedmethods and including nano-diamond particles having a particle size offrom about 1 nm to about 100 nm dispersed in a dispersion solvent.

The nano-diamond particles may have an average particle diameter of fromabout 9 nm to about 90 nm.

The nano-diamond particles may include a metal ion and a reactive groupchemically bonded to a surface thereof.

The nano-diamond particles may further include a metal hydroxideadsorbed on a surface thereof.

The dispersion solvent may include at least one of water, distilledwater, alcohol, oil, an organic solvent, hydrogen peroxide, ammoniawater, toluene, xylene, ethylene glycol, methylethylketone (MEK), andn-methyl pyrrolidone (NMP).

According to an aspect of the present invention, there is provided asealing agent for use in anodization, including a nano-diamonddispersion prepared using any of the above-described methods andincluding nano-diamond particles having a particle size of from about 1nm to about 100 nm dispersed in a dispersion solvent.

The nano-diamond particles in the sealing agent may have an averageparticle diameter of from about 9 nm to about 90 nm.

The nano-diamond particles in the sealing agent may include a metal ionand a functional group chemically bonded to a surface thereof.

The nano-diamond particles in the sealing agent may further include ametal hydroxide adsorbed on a surface thereof.

According to an aspect of the present invention, there is provided apolishing is agent including a nano-diamond dispersion prepared usingany of the above-described methods and including nano-diamond particleshaving a particle size of from about 1 nm to about 100 nm dispersed in adispersion solvent.

According to an aspect of the present invention, there is provided anoil additive including a nano-diamond dispersion prepared using any ofthe above-described methods and including nano-diamond particles havinga particle size of from about 1 nm to about 100 nm dispersed in adispersion solvent.

According to an aspect of the present invention, there is provided apolymer resin additive including a nano-diamond dispersion preparedusing any of the above-described methods and including nano-diamondparticles having a particle size of from about 1 nm to about 100 nmdispersed in a dispersion solvent.

Advantageous Effects

According to the embodiments of the present invention, using the methodof preparing a nano-diamond dispersion described above, a nano-diamonddispersion of uniformly dispersed nano-diamond particles having aparticle size of from about 1 nm to about 100 nm may be obtained.

According to the one or more embodiments of the present invention, thenano-diamond dispersion itself may be used as a coating material, alubricating oil additive, a plating material, such as a sealing agent inanodization, or an additive in plating or surface treatment with nickel,chromium, gold, silver, or the like. The nano-diamond dispersion may beadded to polymer plastic, a paint additive, a material forheat-dissipating products, ceramic hybrid, textile, paper, toothpaste,shampoo, soap, cosmetics, or the like to improve functionality.Furthermore, a surface functionalized nano-diamond compound may be usedas a starting material in preparing a nanobio material-basedpharmaceutical material.

A nano-diamond composition prepared by using a matrix of thenano-diamond colloid dispersion such as a polymer resin, a syntheticpolymer, a protein, a metal, an alloy or the like may be applicable to apromising composite material due to the inclusion of diamond havinginherent advantageous characteristics. In the is nano-diamonddispersions according to the embodiments of the present invention,nano-diamond particles are uniformly dispersed and not clustered oraggregated together, and thus have an increased contact area withmatrix. This may result in an effective mixing.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of a method of preparing a nano-diamonddispersion, according to an embodiment of the present invention;

FIG. 2 is a schematic diagram illustrating the method of preparing anano-diamond dispersion in FIG. 1;

FIG. 3 is a flowchart of a method of processing a precipitate in FIG. 1;

FIG. 4 shows images of a nano-diamond dispersion according to anembodiment of the present invention, and a nano-diamond aggregationsolution as a comparative example;

FIG. 5 is a graph comparing particle size distributions of nano-diamondparticles in the nano-diamond dispersion according to an embodiment ofthe present invention and that of the nano-diamond aggregations in thenano-diamond aggregation solution of the comparative example;

FIGS. 6 and 7 are graphs obtained from X-ray photoelectron spectroscopyon the NaOH-nano-diamond dispersion (present invention) and theNaCl-nano-diamond dispersion (comparative example), respectively;

FIG. 8 is a graph of particle size distributions in a nano-diamonddispersion according to an embodiment of the present invention and anano-diamond dispersion of a comparative example;

FIG. 9 shows images of the nano-diamond dispersions of FIG. 8;

FIG. 10 is a graph of particle size distributions in a nano-diamonddispersion according to an embodiment of the present invention and anano-diamond dispersion of a comparative example; and

FIG. 11 shows images of the nano-diamond dispersions of FIG. 10.

BEST MODE

The present invention will now be described more fully with reference tothe accompanying drawings, in which exemplary embodiments of theinvention are shown. The invention may, however, be embodied in manydifferent forms and should not be construed as being limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the concept of the invention to those skilled in the art.

FIG. 1 is a flowchart of a method of preparing a nano-diamonddispersion, according to an embodiment of the present invention. FIG. 2is a schematic diagram illustrating the method of preparing anano-diamond dispersion in FIG. 1.

Referring to FIGS. 1 and 2, a nano-diamond aggregation 10 is provided(S10). The nano-diamond aggregation 10 may be prepared using any one ofa high-temperature high-pressure method, a shock-wave method, chemicalvapor deposition (CVD), and an explosion method. For example, accordingto the explosion method, nano-diamond aggregations may be prepared in ahigh-temperature high-pressure atmosphere induced by exploding anexplosive such as trinitrotoluene (TNT), or a research departmentexplosive (RDX) as a white, crystalline, water-insoluble bomb. Thenano-diamond aggregation 10 may have a size of several hundreds ofnanometers to several thousands of nanometers. In addition, impuritiessuch as cluster carbon or regenerated surface graphite may be removedfrom the nano-diamond aggregation 10 by using an acid, for example,nitric acid or hydrochloric acid.

To disperse the nano-diamond aggregation 10, the nano-diamondaggregation 10 may be mixed with an aqueous solution of metal hydroxidewhile agitating to obtain a mixture solution 20 (S20). A metal componentin the metal hydroxide may be any element that has a higher ionizationtendency than hydrogen H. For example, the metal component may be atleast one of potassium (K), calcium (Ca), sodium (Na), magnesium (Mg),aluminum (Al), zinc (Zn), iron (Fe), nickel (Ni), tin (Sn), and lead(Pb). The aqueous solution of metal hydroxide may include, for example,NaOH, KOH, or a mixture thereof. The metal hydroxide may change surfacecharacteristics of the is nano-diamond. For example, a reactionmechanism of the nano-diamond and the metal hydroxide may be representedby Formula 1 below, wherein “M” denotes a metal element.C—COOH+MOH=>C—COO⁻M⁺+H₂O  Formula 1

According to Formula 1 above, with the substitution of hydrogen with ametal ion, electrical repulsion between nano-diamond particles in thenano-diamond aggregation is increased, thus dispersibility in a solutionmay be increased. The larger the ionic diameter of the metal ion, thelower the initial precipitation rate. In Formula 1, a carboxyl group(—COOH) on the surface of the nano-diamond is denoted to chemically bindwith the metal ions. However, the present invention is not limitedthereto, and other various reactive groups may exist on the surface ofthe nano-diamond, for example, a hydroxyl group (—OH), an alcohol group(CH₂OH), an amine group (—NH₂), an amide group (—NHCOCH₃), an amidegroup (—CONH), a sulfone group (COSO₃H), a sulfonyl chloride group(COSO₂Cl), a methyl(—CH₃), an aldehyde group (—CHO), and an ether group(—O—), wherein at least some of these groups may be chemically bonded tothe metal ions. Formula 2 below represents a chemical reaction when ahydroxyl group (—OH) is on the surface of the nano-diamond, wherein ahydrogen ion of the hydroxyl group (—OH) is substituted with a metal ionof a metal hydroxide.C—OH+MOH=>C—O⁻M⁺+H₂O  Formula 2

The metal hydroxide may be adsorbed onto the surface of the nano-diamondparticles by van der Waals force. The adsorbed metal hydroxide mayfurther increase electrical repulsion between the nano-diamondparticles, thus further improving dispersability in a solution.

The agitating may be performed using a common method. For example, theagitating may be achieved using a stirrer 2, such as a rod, which isplaced in a solution for agitation, or using ultrasonic waves. Theagitating may help the nano-diamond aggregation 10 and the aqueous metalhydroxide solution to be more uniformly mixed. The agitation temperatureand time may be dependent on the size of the nano-diamond is aggregation10 and the type of metal element used. For example, the agitating may beperformed at a temperature of from about 30° C. to about 110° C., and insome embodiments, may be performed at a temperature of from about 80° C.to about 100° C. For example, the agitation time may be performed forabout 1 second to about 24 hours, and in some other embodiments, may befor from about 10 hours to about 14 hours. The mixture solution 20 mayhave a pH of greater than 7 (i.e., alkaline), or a pH of less than 7(i.e., acidic). For example, the mixture solution 20 may have a pH ofabout 8 to 10, and in some embodiments, may have a pH of about 3 to 6.This pH variation of the mixture solution 20 is attributed to that theaqueous metal hydroxide solution is alkaline and the nano-diamondaggregation 10 is acidic in general. Therefore, the pH of the mixturesolution 20 is dependent on relative amounts of the aqueous metalhydroxide solution and the nano-diamond aggregation 10.

The preparation of the mixture solution 20 (S20) may further includedisintegrating the nano-diamond aggregation 10 using a centrifuge, aball mill, a bead mill, or an ultrasonicator. The nano-diamondaggregation 10 in the mixture solution 20 may be disintegrated intoindividual nano-diamond particles. The disintegrating may be performedusing, for example, a centrifuge 3. For example, the centrifugationspeed may be from about 5,000 rpm to about 20,000 rpm, and in someembodiments, may be from about 6000 rpm to about 10000 rpm. For example,the centrifugation time may be from about 1 second to about 24 hours,and in some embodiments, may be from about 1 minute to about 30 minutes.The disintegrating may be performed by ball milling or bead milling. Inball milling or bead milling, the sizes of balls or beads may range fromabout 0.1 mm to about 0.3 mm. The disintegrating may be performing usingan ultrasonicator.

Subsequently, the mixture solution 20 is stabilized (S30). Thestabilizing may include leaving the mixture solution 20 for a whilewithout stirring or vibrating. In some embodiments, the stabilizationtime may be from about 1 second to about 24 hours. Through thestabilization, the mixture solution 20 may be separated into asupernatant 30 and a precipitate 40.

The supernatant 30 and the precipitate 40 are extracted from the mixtureis solution 20, respectively (S40). For example, a size (e.g., particlediameter) of the nano-diamond particles in the supernatant 30 may befrom about 1 nm to about 100 nm, and in some other embodiments, may befrom about 5 nm to about 40 nm. The supernatant 30 may have a pH of, forexample, from about 7.5 to about 8.5. A size of the nano-diamondparticles in the precipitate 40 may be greater than about 40 nm. Forexample, the nano-diamond particles may have an average particlediameter of from about 9 nm to about 90 nm, and in some embodiments, maybe from about 9 nm to about 30 nm. The average particle diameter of thenano-diamond particles may be dependent on the type and amount ofchemical components included in the nano-diamond aggregation, and/or thepH of the aqueous metal hydroxide solution. In particular, thenano-diamond particles tend to have a larger average particle diameterwhen the aqueous metal hydroxide solution is acidic, and to have asmaller average particle diameter when the aqueous metal hydroxidesolution is alkaline.

The supernatant 30 may be a nano-diamond dispersion. The supernatant 30may contain the nano-diamond particles and the metal ions chemicallybonded to the nano-diamond particles. The supernatant 30 may furtherinclude the metal hydroxide adsorbed on the surface of the nano-diamondparticles.

The supernatant 30 may be dried in a furnace or a dry oven to obtainnano-diamond powder (S50). This drying is optional. For example, thedrying temperature may be from about 100° C. to about 600° C., and insome embodiments, may be from about 300° C. to about 500° C. Forexample, the drying time may be from about 1 minute to about 24 hours,and in some embodiments, may be from about 2 hours to 3 hours. Thenano-diamond powder may further contain the metal ion chemically bondedthereto, and the metal hydroxide adsorbed to the surface thereof.

The dried nano-diamond powder may be mixed with a dispersion solvent(S60). This mixing is optional. The mixing may be performed usingultrasonic waves and/or a bead milling apparatus. For example, themixing by ultrasonication may be performed for about 1 minute to about 2hours, and in some embodiments, may be from about 10 minutes to about 1hour. As a result, a nano-diamond dispersion 50 is obtained. Thenano-diamond dispersion 50 may have any of a variety of concentrations.The nano-diamond dispersion 50 may have a pH of about 7. For example,the is nano-diamond dispersion 50 may have a pH of about 3 to 13, and insome embodiments, may have a pH of about 6 to about 8. The nano-diamonddispersion 50 may be acidic, alkaline, or neutral. A size of thenano-diamond particles in the nano-diamond dispersion 50 may be fromabout 1 nm to about 100 nm, and in some embodiments, may be from about 5nm to about 40 nm.

Non-limiting examples of the dispersion solvent are water, distilledwater, alcohol, oil, organic solvent, hydrogen peroxide, and ammoniawater. Non-limiting examples of the organic solvent are toluene, xylene,ethylene glycol, methylethylketone (MEK), and n-methyl pyrrolidone(NMP), which is for illustrative purposes only, and the presentinvention is not limited thereto.

The nano-diamond dispersion 50 may contain the nano-diamond particlesand the metal ion chemically bonded to the nano-diamond. The supernatant50 may further contain the metal hydroxide adsorbed on the surface ofthe nano-diamond particles.

The nano-diamond powder obtained through drying may aggregate to someextent, but may disperse when mixed with a dispersion solvent such asdistilled water. This is attributed to chemical binding of the reactivegroups and the metal ions on the surface of the nano-diamond powder,which enhances dispersion of the nano-diamond powder. The metalhydroxide adsorbed on the surface of the nano-diamond powder may furtherenhance dispersion of the nano-diamond powder.

FIG. 3 is a flowchart of a method of processing the precipitate 40 ofFIG. 1.

Referring to FIG. 3, the precipitate 40 may be added back into themixture solution 20 and agitated together (S45). The agitating may beperformed in the same condition as in the preparing of the mixturesolution 20 (S20), followed by the subsequent processes. This processperformed on the precipitate 40 is optional.

Hereinafter, nano-diamond dispersions according to embodiments of thepresent invention will be described in greater detail in comparison witha mixture solution of nano-diamond aggregation.

FIG. 4 shows images of a nano-diamond dispersion according to anembodiment of the present invention, and a mixture solution of anano-diamond aggregation as a is comparative example. In FIG. 4, (a) isan image of the nano-diamond dispersion according to an embodiment ofthe present invention after being left for 60 days, and (b) is an imageof a solution of nano-diamond aggregation from operation S10 of FIG. 1mixed with distilled water, as a comparative example taken after 1 dayafter being mixed with the distilled water. Both the nano-diamonddispersion and the nano-diamond aggregation solution were prepared tohave a nano-diamond concentration of about 0.1 wt %.

Referring to FIG. 4, the nano-diamond dispersion was found to form auniform nano-diamond dispersion in a solution (see region A) with almostno precipitate even after being left 60 days. On the contrary, thenano-diamond aggregation solution was separated into a solvent (regionB) and the nano-diamond aggregation (region C) after only 1 day.Therefore, the nano-diamond dispersion according to an embodiment of thepresent invention may provide higher, long-term dispersion stabilityrelative to the nano-diamond aggregation solution.

FIG. 5 is a graph comparing particle size distributions of thenano-diamond particles in the nano-diamond dispersion according to anembodiment of the present invention and that of the nano-diamondaggregations in the nano-diamond aggregation solution. The graph of FIG.5 illustrates a measurement result performed using a nanoparticle sizeanalyzer. According to the operational principle of the nanoparticlesize analyzer, dynamic light scattering (DLS) is used to measure theparticle sizes. When particles or molecules are irradiated by a laserbeam, because relatively small particles tend to be moved farther awayand faster by solvent molecules, the intensity of scattered light variesin proportion to the size of particles. The particle size distributionmay be obtained by calculating the speed of Brownian motion throughanalysis of these intensity variations.

Referring to FIG. 5, a particle size of the nano-diamond particles inthe nano-diamond dispersion may be from about 1 nm to about 100 nm, andin some embodiments, may be from about 5 nm to about 40 nm, and in someother embodiments, may be about 9.95 nm on average. The term “particlesize” may refer to the sizes of individual nano-diamond particles, orthe sizes of clusters of the nano-diamond particles. A particle size ofthe nano-diamond aggregation may be from is about 200 nm to about 1000nm, and in some embodiments, may be about 330 nm on average. Accordingto embodiments of the present invention, the nano-diamond dispersion maycontain smaller nano-diamond particles than the nano-diamond aggregationsolution.

Hereinafter, a nano-diamond dispersion according to an embodiment of thepresent invention that is prepared from the mixture solution usingsodium hydroxide (NaOH) as a metal hydroxide, and a nano-diamonddispersion as a comparative example prepared using a sodium chloride(NaCl) solution will be described in detail. According to thecomparative example, in operation S20 described above, the nano-diamondaggregation was mixed with a sodium chloride (NaCl) solution to obtain amixture solution, followed by operations S30-S60 to obtain thenano-diamond dispersion. A nano-diamond concentration of thenano-diamond dispersion was about 1 wt %. For convenient distinction,the nano-diamond dispersion according to the embodiment of the presentinvention is referred to as a NaOH-nano-diamond dispersion, and thenano-diamond dispersion of the comparative example is referred to as aNaCl-nano-diamond dispersion.

Table 1 is a component analysis table of the NaOH-nano-diamonddispersion and the NaCl-nano-diamond dispersion, obtained using energydispersion spectroscopy (EDS).

TABLE 1 Wt % Na Cl NaOH-nano-diamond dispersion 0.7 NoneNaCl-nano-diamond dispersion 0.79 0.54

The NaOH-nano-diamond dispersion and the NaCl-nano-diamond dispersionhad similar sodium contents. In addition, the NaCl-nano-diamonddispersion had a chlorine content of about 0.54 wt %, while theNaOH-nano-diamond dispersion contained no chlorine. According to thecomparative example using the NaCl solution in the mixture solution,chlorine also remains in the final nano-diamond dispersion.

FIGS. 6 and 7 illustrate results of X-ray photoelectron spectroscopy forthe NaOH-nano-diamond dispersion (present invention) and theNaCl-nano-diamond dispersion (comparative example), respectively.

Referring to FIGS. 6 and 7, there was no chlorine in theNaOH-nano-diamond dispersion, while there was chlorine in theNaCl-nano-diamond dispersion, which is the same result of the EDSdescribed above.

Chlorine may reduce dispersibility of nano-diamond and is likely tocause a defect by oxidizing a sealed or polished material. Accordingly,it is advantageous to remove chlorine from a nano-diamond dispersion. Inthis regard, the NaOH-nano-diamond dispersion according to an embodimentof the present invention containing no chloride may have bettercharacteristics than the NaCl-nano-diamond dispersion as a comparativeexample.

FIG. 8 illustrates a graph of particle size distribution in anano-diamond dispersion according to an embodiment of the presentinvention and a nano-diamond dispersion as a comparative example. FIG. 9shows images of the nano-diamond dispersions of FIG. 8. The nano-diamonddispersion according to the embodiment of the present invention is aNaOH-nano-diamond dispersion, and the nano-diamond dispersion as acomparative example is a NaCl-nano-diamond dispersion. The graph of FIG.8 is the results obtained using a nanoparticle size analyzer.

Referring to FIG. 8, the nano-diamond particles in the NaOH-nano-diamonddispersion had an average particle size (e.g., particle diameter) ofabout 20.4 nm. Nearly no nano-diamond particles having a particle sizeof 100 nm or greater were found. In some embodiments of the presentinvention, the NaOH-nano-diamond dispersion may have a particle size(e.g., particle diameter) of from about 1 nm to about 100 nm, and insome other embodiments, may have a particle size of from about 1 nm toabout 70 nm. The particle size may refer to the sizes of individualnano-diamond particles, or the sizes of clusters of the nano-diamondparticles. A particle size of the nano-diamond particles in theNaCl-nano-diamond dispersion may be from about 200 nm to about 6,000 nm,or may be about 1,280 nm on average. Therefore, the nano-diamonddispersions according to the embodiments of the present invention mayhave a smaller nano-diamond particle size than the NaCl-nano-diamonddispersions described above as comparative examples.

Referring to FIG. 9, the NaOH-nano-diamond dispersion is seen to be auniform nano-diamond dispersion (see region A). In addition, theNaCl-nano-diamond is dispersion is separated into a solvent (region B)and a nano-diamond precipitate (region C). The NaOH-nano-diamonddispersion had nearly no change in dispersion stability even afterstorage for about 60 days or longer. Therefore, the nano-diamonddispersions according to the embodiments of the present invention mayprovide higher, long-term dispersion stability relative to theNaCl-nano-diamond dispersion using an NaCl solution.

Hereinafter, a nano-diamond dispersion according to an embodiment of thepresent invention that is prepared from the mixture solution usingpotassium hydroxide (KOH) as a metal hydroxide, and a nano-diamonddispersion as a comparative example prepared using a potassium chloride(KCl) solution will be described in detail. According to the comparativeexample, in operation S20 described above, the nano-diamond aggregationwas mixed with a potassium chloride (KCl) solution to obtain a mixturesolution, followed by operations S30-S60 to obtain the nano-diamonddispersion. A nano-diamond concentration of the nano-diamond dispersionwas about 1 wt %. For convenient distinction, the nano-diamonddispersion according to the embodiment of the present invention isreferred to as a KOH-nano-diamond dispersion, and the nano-diamonddispersion of the comparative example is referred to as aKCl-nano-diamond dispersion.

FIG. 10 is a graph of particle size distributions in a nano-diamonddispersion according to an embodiment of the present invention and anano-diamond dispersion as a comparative example. FIG. 11 shows imagesof the nano-diamond dispersions of FIG. 10. The nano-diamond dispersionaccording to the embodiment of the present invention is aKOH-nano-diamond dispersion, and the nano-diamond dispersion as acomparative example is a KCl-nano-diamond dispersion. The graph of FIG.10 is the results obtained using a nano particle size analyzer.

Referring to FIG. 10, the nano-diamond particles in the KOH-nano-diamonddispersion had an average particle size (e.g., particle diameter) ofabout 29.0 nm. Nearly no nano-diamond particles having a particle sizeof 150 nm or greater were found. In some embodiments of the presentinvention, the KOH-nano-diamond dispersion may have a particle size(e.g., particle diameter) of from about 1 nm to about 150 nm, and insome other embodiments, may have a particle size of from about 1 nm isto about 100 nm. The particle size may refer to the sizes of individualnano-diamond particles, or the sizes of clusters of the nano-diamondparticles. A particle size of the nano-diamond particles in theKCl-nano-diamond dispersion may be from about 400 nm to about 6,000 nm,or may be about 1,450 nm on average. Therefore, the nano-diamonddispersion according to the embodiment of the present invention may havea smaller nano-diamond particle size than the KCl-nano-diamonddispersion described above as a comparative example. In comparison withthe graph of FIG. 8, the NaOH-nano-diamond dispersion of FIG. 8 wasfound to have a smaller particle size than the KCl-nano-diamonddispersion of FIG. 10, indicating that NaOH may have a betternano-diamond dispersing effect than KOH.

Referring to FIG. 11, the KOH-nano-diamond dispersion is seen to be auniform nano-diamond dispersion (see region A). In addition, theKCl-nano-diamond dispersion is separated into a solvent (region B) and anano-diamond precipitate (region C). The KOH-nano-diamond dispersion hadnearly no change in dispersion stability even after storage for about 60days or longer. Therefore, the nano-diamond dispersions according to theembodiments of the present invention may provide higher, long-termdispersion stability relative to the KCl-nano-diamond dispersion using aKCl solution.

MODE OF THE INVENTION

The present invention will now be described more fully with reference toan exemplary embodiment using a nano-diamond dispersion according to anembodiment of the present invention described above in a sealing agent.The invention may, however, be embodied in many different forms andshould not be construed as being limited to the embodiments set forthbelow.

An oxide film formed through anodization is porous, highly adsorptive,and apt to be discolored when dyed. To address these drawbacks,anodization involves sealing as a final process. Such an oxide filmformed by anodization is initially highly reactive enough to adsorb gasor the like in the air when left alone, to become inactive. For thisreason, sealing is performed to stabilize the oxide film. Sealing isperformed by is filling pores in the oxide film so as to modify filmcharacteristics in terms of, for example, corrosion resistance. Existingsealing processes may be performed by hydration, by using a metal saltor an organic material, by coating, or the like. In particular, themetal salt sealing using a metal salt is a process of filling pores viaa hydrolysis of a metal salt solution having flowed into the holes toform a hydroxide precipitate. As common metal salts for sealing, acidcomplex of nickel and acid complex of cobalt have been used and thesematerials are currently listed as environmentally toxic materials andprohibited from use. Therefore, there is a demand for the development ofa new sealing technique.

A sealing agent according to an embodiment of the present inventionincludes a nano-diamond dispersion prepared according to any of theabove-described methods and having a nano-diamond particle size of fromabout 1 nm to about 100 nm. The nano-diamond particles include metalions and reactive groups chemically bonded to the surfaces thereof. Thenano-diamond particles in the sealing agent are fine enough, highlystable, and uniformly dispersed in the nano-diamond dispersion, and thusare suitable to reliably seal pores in an oxide film. Sealing with thesealing agent may improve corrosion resistance of the oxide film,anti-contamination ability, stability of dyed or colored oxide films,and resistance to light (resistance to weather). Furthermore, this mayreduce use of environmentally toxic materials used so far.

In some embodiments of the present invention, a nano-diamond dispersionaccording to any of the above-described embodiments may be used in apolishing agent, an oil additive, a polymer resin additive, and thelike. The polishing agent including a nano-diamond dispersion accordingto any of the embodiments of the present invention may be applicable in,for example, metal processing or when processing a semiconductor wafer.The polishing agent may be used in chemical mechanical polishing (CMP).The polishing agent including the above-described nano-diamonddispersion may reduce unwanted scratching, achieve a high level offlatness, and reduce residual stress.

In some embodiments, the oil additive including the nano-diamonddispersion according to any of the above-described embodiments of thepresent invention may be a lubricating oil additive used in machines orvehicles. The lubricating oil including the is above-describednano-diamond dispersion may reduce a frictional moment at a contactsurface by about 20% to about 40%, consequently suppressing atemperature rise in a contact area and reducing abrasion of mechanicalparts.

In some embodiments, the resin additive including a nano-diamonddispersion according to any of the above-described embodiments of thepresent invention may be a polymer resin additive used in preparingpolymer resin, for example, urethane, epoxy, or polyvinylalcohol (PVA).The resin including the above-described nano-diamond dispersion mayimprove elasticity, heat resistance, cold resistance, and chemicalresistance, and reduce a coefficient of friction.

In some embodiments, a heat-dissipating additive including anano-diamond dispersion according to any of the above-describedembodiments of the present invention may appropriately dissipate andhold heat, and thus be applicable as a surface coating material for carradiators, or a heat dissipating material for an LED and aheat-dissipating plate of laptop computers.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

INDUSTRIAL APPLICABILITY

According to the one or more embodiments of the present invention, thenano-diamond dispersion itself may be used as a coating material, alubricating oil material, a plating material, such as a sealing agent inanodization, or an additive in plating or surface treatment with nickel,chromium, gold, silver, or the like. The nano-diamond dispersion may beadded to polymer plastic, a paint additive, a material forheat-dissipating products, polymer plastic, ceramic hybrid, textile,paper, toothpaste, shampoo, soap, cosmetics, or the like to providefunctionality. Furthermore, a surface functionalized nano-diamondcompound may be used as a starting material in preparing a nanobiomaterial-based pharmaceutical material.

The invention claimed is:
 1. A method of preparing a nano-diamonddispersion, the method comprising: providing a nano-diamond aggregation;mixing the nano-diamond aggregation and an aqueous metal hydroxidesolution while agitating to prepare a mixture solution in order todisintegrate the nano-diamond aggregation; stabilizing the mixturesolution to be separated into a supernatant and a precipitate; andextracting the supernatant and the precipitate respectively from themixture solution.
 2. The method of claim 1, further comprising, afterthe extracting of the supernatant and the precipitate from the mixturesolution, drying the supernatant to obtain nano-diamond powder; andmixing the nano-diamond powder with a dispersion solvent.
 3. The methodof claim 1, further comprising, after the extracting of the supernatantand the precipitate from the mixture solution, adding the precipitateback into the mixture solution while agitating.
 4. The method of claim1, wherein the preparing of the mixture solution further comprisesdisintegrating the nano-diamond aggregation using a centrifuge, a ballmill, a bead mill, or an ultrasonicator.
 5. The method of claim 1,wherein the aqueous metal hydroxide solution comprises at least one ofpotassium (K), calcium (Ca), sodium (Na), magnesium (Mg), aluminum (Al),zinc (Zn), iron (Fe), nickel (Ni), tin (Sn), and lead (Pb).
 6. Themethod of claim 1, wherein the aqueous metal hydroxide solutioncomprises NaOH, KOH, or a mixture thereof.
 7. The method of claim 1,wherein the preparing of the mixture solution comprises chemicallybinding a metal ion in the aqueous metal hydroxide solution and afunctional group in the nano-diamond aggregation.
 8. The method of claim7, wherein the functional group comprises at least one of a carboxylgroup (—COOH), a hydroxyl group (—OH), an alcohol group (CH2OH), anamine group (—NH2), an amide group (—NHCOCH3), an amide group (—CONH), asulfone group (COSO3H), a sulfonyl chloride group (COSO2Cl), a methylgroup (—CH3), an aldehyde group (—CHO), and an ether group (—O—).